Cable art has become a major concern to audiophiles. In comparatively recent times, the cable has been considered in itself an integral component of a high quality or so-called "high-end" audio system rather than merely a sonically neutral link between equipment. The present invention relates to a power cable for installation in power supply sections of audio equipment, and it is ideally suited for use with high current power amplifiers.
The cable art has been concerned hitherto with the transmission of electrical signals along the signal path; that is, from source inputs such as phonograph players, tuners, and CD players, to preamplifiers and power amplifiers, and from power amplifiers to loudspeakers. The cables which electrically link audio equipment along the signal path have been referred to as "interconnects". Of primary concern has been the skin effect, whereby signals traveling at the "skin" or farthest radial distance from the center of a conductor induce time shifts in signals traveling near the center of the conductor. U.S. Pat. No. 4,767,890 ("Magnan"), incorporated herein by reference, addresses the so-called "skin effect" problem in interconnect cables, including cables used to connect amplifiers to speakers, which transmit broad-band audio signals. Magnan teaches that when signals at audio frequencies are transmitted through prior art cables comprising a plurality of conductors, the high frequency components propagate along conductors on the outside of the cable and travel at a faster speed than the lower frequency components which propagate along the conductors at the center of the cable and travel at a lower speed. The signals of the various components arrive at and drive the speakers at different times, and result in a "smearing" of the reproduced sound signal.
The Magnan patent discloses the use of a twin-axial pair of cables comprising a number of insulated conductors spiralled helically around a large diameter air core and within a spirally wrapped dielectric tube spacer to approximate a pair of thin conducting cylinders. The preferred embodiment consists of one 84-gauge, three 37-gauge, and three 40-gauge oxygen-free copper conductors and five 26-gauge TFE Teflon tubes, all shielded within a braided shield and a cable jacket. An external, shielded ground return for conducting higher levels of DC is provided outside of the main shielded cable. As will be appreciated by those skilled in the art, the Magnan approach is better than the standard multistranded wire for transmitting broad-band signals. However, the Magnan approach does not teach or indicate how to construct a compact, relatively inexpensive cable for use as a power cable for transmitting high current at 60 Hz at uniform density free from phase delays.
The audiophile industry has not sufficiently focused upon the construction of "audiophile power cables". U.S. Pat. No. 3,261,907, incorporated herein by reference, is a rare example in which the internal inductive effects of current have been considered in the area of power cables, and expressly provides for a cable for high frequency systems, specifically the 400-cycle system used in the power circuits for aircraft and surface ships, but not, however, to the standard 60-cycle system dear to the audiophile. The cable disclosed therein is merely intended to overcome the electrical difficulties presented by high frequency polyphase circuits by using cables with multiple conductors concentrically arranged and interposed with concentric layers of insulation. However, the '907 reference does not disclose or instruct how a power cable is to be used in a standard 60-cycle system which presents its own self-inductance problems when used in high current audiophile applications. Nor does it suggest, because it does not consider, the "esoteric" sonic concerns of audiophiles.
For current of any given frequency travelling along a conductor, a "skin effect" or inductance problem arises whereby current travelling at the outer radial dimensions of a conductor generates a field which electromagnetically inhibits current traveling near the core of the conductor. The effect is such that current arriving at the end of the typical power cable, i.e. lamp cord, attached to the power supply section of a power amplifier suffers from phase delay. This effect is that the current in the center of the wire is less than the amount of current travelling at the outer radial portions of the conductor. While a person of ordinary skill in the art might question the sonic effect to be derived from a cord which lies beyond the signal path and which, moreover, is intended to transfer current at one frequency (60-Hz), there are indeed insignificant sonic problems which the present invention unexpectedly redresses.
High current amplifiers are increasingly being used by audiophiles for their ability to drive high impedance loads, typically loudspeakers presenting 4 ohms or less per stereophonic side, New speaker technologies, such as electrostatic speakers, or planar speakers in which current must be passed through microscopic wires suspended in mylar diaphragms across magnetic fields, frequently present difficult loads for which the ability to transfer high current instantly, uniformly, and continuously is required. Even with loudspeakers employing conventional 8 ohm piston-driven transducers, difficult loads are presented by complex electronic cross-overs, driver arrays, and musical signals which may contain highly complex waveforms extending throughout the broad-band audio spectrum. Moreover, with recent improvements in source components such as CD players and turntables equipped with high output moving coil cartridges, it is desirable to have amplifiers and power supplies provide high amounts of current instantaneously, uniformly, and consistently for accurate and high-resolution reproduction of transient information, even at low listening volumes. The demand for the desired capabilities of transferring high current is even necessary for amplifiers or power supply stages which are regulated and have large filter capacitors, since sudden power drains may occur requiring that a power cable provide surges of current up to 20 amperes instantly without self-induced phase delays or ripple effects in the 60 Hz line.
An "audiophile" power cable is therefore needed in view of the foregoing demands and disadvantages explained above.